Can y’all help pls ;)

One-third of the people from country a claim that they are from country b, and the rest admit they are from country a. one-fourth of the people from country claim that they are from country a, and the rest admit they are from country b. in a combined census of the two countries, one-half of the total claimed to be from a. what is the ratio of the populations of country a to that of country b.

Asap! i'm not good math and i'm lost.

X^2/100+y^2/25=1 the length of the major axis is: a)5 b)10 c)20